1. Field of the Invention
The present invention relates to a magnetic head slider, and more particularly to the construction of a protective film and a seed layer for the protective film formed on an air bearing surface.
2. Description of the Related Art
In a hard disk drive (HDD), data are read from a recording medium (a hard disk or a magnetic disk) and are written to a recording medium while a magnetic head slider (hereinafter referred to as a slider) glides over the recording medium with a small gap.
A slider that reads data from the recording medium and that writes data to the recording medium is required to be free from corrosion in various environmental conditions, and is also required to be protected from collision against the recording medium. For this purpose, a protective film formed of diamond-like carbon (DLC) is formed on a surface of a slider body that is opposite to the recording medium, i.e., the air bearing surface. In order to improve adhesion of the protective film to the slider body, a seed layer, for example formed of silicon, is formed between the protective film and the slider body. In this specification, the slider body refers to the portion of the slider that does not include the seed layer and the protective film, i.e., the portion of the slider that includes a substrate thereof and elements, such as a write head element, a read head element and insulating layers, formed on the substrate in the wafer process.
As a result of the recent increase in recording density of recording media, a further reduction in the distance between the slider and the recording medium has been required. More precisely, this means a reduction in the distance between the read head element and the recording medium and in the distance between the write head element and the recording medium. Therefore, an increase in the recording density requires reducing the flying height, as well as reducing the thicknesses of the protective film and the seed layer. The reduction in the flying height has progressed over long years based on the method called the dynamic flying height. On the other hand, since the protective film and the seed layer are formed on the surface of the slider body which is made irregular because of lapping etc, the film thicknesses of the protective film and the seed layer can be easily affected and may be made uneven due to the irregularities. Portions of the protective film having thinner film thicknesses may easily develop pin holes which may cause corrosion in the read head element and the write head element lying below the pin holes. Therefore, it is difficult to simply reduce the film thicknesses of the protective film and the seed layer in order to reduce the distance between the slider and the recording medium.
Japanese Patent Publication No. 1994-12615 discloses a magnetic head having a protective film, such as a DLC film, and a seed layer under the protective film, the seed layer comprising one or more elements selected from a group consisting of silicon, chromium etc. The art disclosed in this document aims at improving adhesion of the protective film to the slider body by means of such a seed layer. Since corrosion also occurs as a result of separation of the seed layer from the slider body, followed by exposure of the slider body, an improvement in adhesion of the seed layer contributes to an improvement in robustness against corrosion. The above-mentioned document also discloses that the seed layer and the protective film each preferably have a thickness of 1 to 5 nm.
Thus, from the viewpoint of securing robustness against corrosion, the lower limit of the film thickness of the seed layer and the protective film is about 1 nm according to the prior art and accordingly, the lower limit of the total thickness of the seed layer and the protective film is about 2 nm. Therefore, limiting the total thickness of the seed layer and the protective film may limit an increase in the recording density when developing a magnetic head slider capable of coping with further increases in the recording density.